Organochlorine Pollutants, Nest-Defense Behavior and Reproductive Success in Merlins

Abstract

-In a population of Merlins nesting on the Canadian prairies, the eggs of females with large DDE burdens had significantly lower quality shells, disappeared more frequently, and hatched less frequently than normal. Few of the behavioral responses of such females to territorial intrusions appeared to be significantly altered. We conclude that the changes in nest site defense which accompany DDE contamination are of minor importance in the associated reproductive failure of falcons. Laboratory studies of the effects of organochlorine pollutants on avian reproduction have frequently revealed behavioral abnormalities in the adults (Jeffries 1971, Peakall and Peakall 1973, Winn 1973, Haegele and Hudson 1977). Studies of heavily contaminated wild birds indicate that behavioral abnormalities may be a significant factor in reproductive failure (Milstein et al. 1970, Snyder et al. 1973, Fyfe et al. 1976, Fox et al. 1978). We present here the first field study in which the behavior of nesting females with various degrees of organochlorine contamination in a single population is compared, and we discuss the relationship to reproductive success. The Merlin (Falco columbarius), like its congener the Peregrine (F. peregrinus), is heavily contaminated with, and sensitive to, organochlorine pollutants (Temple 1972, Fyfe et al. 1976, Newton et al. 1978, Fox 1979). Over the past decade the Canadian Wildlife Service has studied contaminant levels and reproductive success of this species on the grasslands of southeastern Alberta. Early in these investigations Fyfe et al. (1976) observed that pairs whose eggs contained high levels of organochlorine pollutants (predominantly p',p'-DDE) deserted their clutches more frequently and defended their nests less actively than less contaminated pairs. In 1975 and 1976, we attempted to quantify these differences.